1. Field of the Invention
This invention relates generally to tool holders and more specifically to a device which attaches an electrode to the quill of an electric discharge machine.
2. Description of the Prior Art
An electric discharge machine brings the surface of an electrode into close proximity with a metal surface that is to be worked on. By developing a voltage between the the electrode and the surface, an electric arc is created which erodes the metal surface so that it assumes the shape of a mirror image of the proximate surface of the electrode. By this technique, shapes of surfaces (such as square holes) can be provided which cannot be obtained with other machining techniques.
Improvements in the technique have been introduced to meet the demand for more intricacy, greater precision, and faster production. These improvements have been achieved, in part, by providing machines that can accurately move the electrode from one location to another and by configuring the electrode holders so that electrodes can be substituted for successive machining operations.
The electrode holder must provide accurate, reproducible positioning of the electrodes. For improved productivity, the electrodes should be able to be quickly replaced.
The quality of the machining operation is also improved by flushing the metal surface with a fluid so as to remove debris generated by the spark erosion process. The stream of fluid should be directed at the point of generation of the electric arc for greatest effectiveness.
A number of prior art patents disclose electrode holders which provide ease of interchange, accurate electrode mounting, or efficient surface flushing. However, no electrode holder disclosed in the prior art provides all three of these features in a single unit.
For example, U.S. Pat. No. 3,711,105 teaches a threaded electrode which is screwed into a bore provided in an electrode holder. The electrode holder has pins which engage holes in the electrode to to provide accurate alignment of the electrode to the holder. U.S. Pat. No. 3,939,322 discloses an electrode provided with a tapered shank which fits into a mating recess provided in an electrode holder. U.S. Pat. No. 3,816,691 teaches a hollow electrode holder through which a flushing fluid is directed, but does not teach a simple, quick, and effective structure for attaching and detaching electrodes.
A common type of electric discharge system is known in the industry as a 3R type system. A problem with 3R type systems is that it requires an expensive blank stem for each electrode.